“The UK nuclear regulator has raised concerns with EDF Energy over management failings that it warns could affect safety at the Hinkley Point C power station if left unaddressed, official documents reveal.

Britain’s chief nuclear inspector identified several shortcomings in the way the French firm is managing the supply chain for the £20bn plant it is building in Somerset.

Though not serious enough alone to raise regulatory issues, together they “may indicate a broader deficiency” in the way the company is run, concluded Mark Foy, chief inspector at the Office for Nuclear Regulation (ONR).

In October and November 2017, a team of 11 inspectors led by Foy visited the Hinkley site, EDF facilities in Bristol and Paris, and a French factory making parts for the plant.

The visits were triggered by the regulator’s concerns that EDF did not have sufficient oversight of the Creusot nuclear forge in France, where records have been found to be falsified.

A summary of the inspections, published by the ONR earlier this month, judged EDF’s supply chain management to be improving but below standard in some areas.

The full reports, released to the Guardian under freedom of information rules, paint a critical picture. They show that:

The ONR was concerned that EDF’s internal oversight and governance had not identified the shortcomings at the forge

Stuart Crook, Hinkley Point C managing director, admitted that EDF, not the ONR, should have spotted those shortcomings first

a lack of resources meant EDF did not undertake an internal audit of its quality control processes during 2017. Foy said this was “disappointing” as it might have picked up problems

On safety, the report said that: “Throughout this … inspection, themes have emerged that relate to both improvements in NNB GenCo’s [the EDF subsidiary building Hinkley] processes and to shortfalls in management system arrangements that, if unresolved, have the potential to affect safety.”

EDF’s own assessment of how it managed Hinkley’s supply chain had discovered shortfalls that could affect safety, the regulator found. The ONR also felt that the company’s plan for improving its self-assessment process was inadequate.

Moreover, they said that it was not clear who at EDF was managing quality control on the supply chain.

Interviews with EDF’s contractors for the Hinkley project, which include civil engineering groups Kier BAM and Bylor, also found that EDF had not done enough to pass on information about the failings at the Creusot forge to its suppliers.

However, the regulator said it was confident the company could make improvements ahead of the next key regulatory milestone for the power station, in August 2018. Overall, EDF was found to be operating within the UK’s exacting nuclear regulations.

“Current arrangements for the control of quality are judged, through ONR’s wider regulatory activities, to be appropriate at present,” said Foy.

Experts said the inspection’s conclusions were significant, as nuclear regulation language is usually restrained.

Paul Dorfman, of the Energy Institute at University College London, said: “Looking at this report with a practiced eye, you can see that the UK regulators are worried, and things aren’t necessarily going to get any better.

“In all things nuclear, safety is absolutely paramount. The fact that the UK nuclear regulator says that these problems could affect safety is very significant.”

EDF said it was already implementing improvement measures where required ahead of an increase in construction activity at the site. The company was also completing the outstanding internal quality assurance programme.

A spokesperson said: “The chief nuclear inspector’s report recognises that the current quality control arrangements for Hinkley Point C are appropriate.”

There are about 3,500 people working on the site at the moment, a number that is expected to peak at around 6,000 in 18 months, when construction is due to be at full throttle.

The power station should provide around 7% of the UK’s electricity and is due to switch on in 2025, though EDF has warned the project may run 15 months over schedule.”